The records feature papers relating to the famous ''Rendlesham Forest'' sightings, often dubbed as ''Britain's Roswell''

Other highlights include:

:: A man arrived at his Birmingham home at 4am on March 20, 1997, to discover an illuminated blue triangle hovering over his garden. The craft shot off leaving behind a ''silky-white'' substance on the tree-tops, which he collected in a jam-jar.

:: A UFO sighted by Boston and Skegness police, in Lincolnshire, was captured on film. The police reported the sighting to the coastguard, who in turn alerted ships in North Sea - where a crew saw more UFOs. Simultaneously, an unidentified blip was picked up on radar over Boston.

:: A request submitted to former Prime Minister John Major from a councillor for an inquiry into 600 alleged sightings in Bonnybridge, Scotland, known as the ''Bonnybridge Triangle''.

:: An object travelling at more than 1,000 knots was tracked by a senior air traffic controller from the control tower at Glasgow Prestwick Airport, in Ayrshire, in February 1999.

:: A West Lothian electrician spotted a ''Toblerone-shaped'' UFO hovering over a field. A sketch of the craft is included in the report.

:: A letter from senior MoD official Ralph Noyes in which he describes seeing a film of UFOs captured by RAF fighter pilots in 1956. Mr Noyes claims the footage was shown at a secret underground screening arranged for Air Defence staff at the MoD Main Building in 1970.

Experts believe the records highlight how shapes of reported UFOs have changed over the last half-century.

This could be explained by representations of UFOs in popular culture - such as TV shows like The X-Files.

Many reports in this latest file describe aircraft as big, black and triangular in shape with lights along the edges, whereas the predominant form in the 1940s to 1950s was saucer or disc-shaped.

Dr David Clarke, author of The UFO Files and senior lecturer in journalism from Sheffield Hallam University said: ''In the 1950s the next big leap in technology was thought to be a round craft that took off vertically and it's intriguing to note that this is the same period when people began to report seeing 'flying saucers' in the sky.

''In the period the latest file release covers, triangular-shaped US stealth bombers and Aurora spy planes featured heavily on TV, such as The X Files between 1993-2002, and films, such as Independence Day released in 1996 and the shape of reported UFOs corresponds.

''It's impossible to prove a direct link between what people are reading and watching and what they report as UFOs but one interpretation could be that the latest advances in technology may be influencing what people see in the sky.''